The onset of light-evoked responsiveness is studied in retina of the Xenopus tadpole in relation to the times at which retinal synapses are formed. Electron microscopy is combined with Golgi-impregnation methods to elucidate neuronal form and synapse ultrastructure. Intracellular recording is utilized to measure light-induced responses of retinal neurons. A second study employs the Vitamin A starved Xenopus tadpole to explore the relation between rod threshold to light and its visual pigment content.